Often extractor fans have a trigger supply and line supply and the latter allows to fan to run on after the trigger is removed. However blue is neutral and brown is line (was black and red) and any other colours should be sleeved to those colours or have a number ID. In practice this is rarely the case but there is of course no standard colour when the rules are broken (even when near everyone breaks them) so sorry you need to have noted what they were connected to or check at source or test them.

Also is it the right type of fan. Part F (I think) stipulates when run on is required and how much air must be moved.

Likely you will need to fold back one wire and tape out of harms way or put into a crimp etc. But much depends on exactly how they are terminated.

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